Plasma curing process for porous silica thin film

ABSTRACT

Low dielectric constant films with improved elastic modulus. An SiO 2 -containing plasma cured coating having a first dielectric constant and having a first elastic modulus is provided, the coating being formed by providing a porous network coating produced from a resin molecule containing at least 2 Si—H groups, and plasma curing the porous network coating to reduce an amount of Si—H bonds. Plasma curing of the network coating yields a coating with improved modulus, but with a higher dielectric constant. Accordingly, an SiO 2 -containing plasma cured coating is also provided, the coating being formed by annealing the plasma cured coating to produce an annealed, plasma cured coating having a second dielectric constant which is less than the first dielectric constant and having a second elastic modulus which is comparable to the first elastic modulus. The annealed, SiO 2 -containing plasma cured coating can have a dielectric constant between about 1.1 and about 3.5 and an elastic modulus greater than or about 4 GPa. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. 37 CFR §1.72(b).

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a division of application Ser. No.09/681,332, filed Mar. 19, 2001 entitled “PLASMA CURING PROCESS FORPOROUS SILICA THIN FILM”, which is a continuation-in-part of applicationSer. No. 09/528,835, filed Mar. 20, 2000 entitled “High Modulus, LowDielectric Constant Coatings”.

BACKGROUND OF THE INVENTION

[0002] This invention relates generally to coatings for use inelectronic devices. More particularly, the invention relates to coatingshaving an improved elastic modulus and a low dielectric constant and tomethods of making such coatings.

[0003] Thin film dielectric coatings on electric devices are known inthe art. For instance, U.S. Pat. Nos. 4,749,631 and 4,756,977, toHaluska et al., disclose silica based coatings produced by applyingsolutions of silicon alkoxides or hydrogen silsesquioxane, respectively,to substrates and then heating the coated substrates to a temperaturebetween 200 and 1000° C. The dielectric constant of these coatings isoften too high for certain electronic devices and circuits.

[0004] U.S. Pat. Nos. 4,847,162 and 4,842,888, to Haluska et al., teachthe formation of nitrided silica coatings by heating hydrogensilsesquioxane resin and silicate esters, respectively, to a temperaturebetween 200 and 1000° C. in the presence of ammonia. These referencesteach the use of anhydrous ammonia so that the resulting coating hasabout 1 to 2% by weight nitrogen incorporated therein.

[0005] Glasser et al., Journal of Non-Crystalline Solids, 64 (1984) pp.209-221, teaches the formation of ceramic coatings by heatingtetraethoxysilane in the presence of ammonia. This reference teaches theuse of anhydrous ammonia and that the resulting silica coatings arenitrided.

[0006] U.S. Pat. No. 4,636,440, to Jada, discloses a method of reducingthe drying time for a sol-gel coated substrate comprising exposing thesubstrate to aqueous quaternary ammonium hydroxide and/or alkanol aminecompounds. Jada requires that the coating be dried prior to heating. Itis specifically limited to hydrolyzed or partially hydrolyzed siliconalkoxides and does not teach the utility of the process on coatingshaving Si—H bonds.

[0007] U.S. Pat. Nos. 5,262,201, to Chandra, and 5,116,637, to Baney etal., teach the use of basic catalysts to lower the temperature necessaryfor the conversion of various preceramic materials, all involvinghydrogen silsesquioxane, to ceramic coatings. These references teach theremoval of solvent before the coating is exposed to the basic catalysts.

[0008] U.S. Pat. No. 5,547,703, to Camilletti et al., teaches a methodfor forming low dielectric constant Si—O containing coatings onsubstrates comprising heating a hydrogen silsesquioxane resinsuccessively under wet ammonia, dry ammonia, and oxygen. The resultantcoatings have dielectric constants as low as 2.42 at 1 MHz. Thisreference teaches the removal of solvent before converting the coatingto a ceramic.

[0009] U.S. Pat. No. 5,523,163, to Balance et al., teaches a method forforming Si—O containing coatings on substrates comprising heating ahydrogen silsesquioxane resin to convert it to a Si—O containing ceramiccoating and then exposing the coating to an annealing atmospherecontaining hydrogen gas. The resultant coatings have dielectricconstants as low as 2.773. The reference teaches the removal of solventbefore converting the coating to a ceramic.

[0010] U.S. Pat. No. 5,618,878, to Syktich et al., discloses coatingcompositions containing hydrogen silsesquioxane resin dissolved insaturated alkyl hydrocarbons useful for forming thick ceramic coatings.The alkyl hydrocarbons disclosed are those up to dodecane. The referencedoes not teach exposure of the coated substrates to basic catalystsbefore solvent removal.

[0011] U.S. Pat. No. 6,231,989, to Chung et al., entitled METHOD OFFORMING COATINGS, discloses a method of making porous network coatingswith low dielectric constants. The method comprises depositing a coatingon a substrate with a solution comprising a resin containing at least 2Si—H groups and a solvent in a manner in which at least 5 volume % ofthe solvent remains in the coating after deposition. The coating is thenexposed to an environment comprising a basic catalyst and water.Finally, the solvent is evaporated from the coating to form a porousnetwork. If desired, the coating can be cured by heating to form aceramic. Films made by this process have dielectric constants in therange of 1.5 to 2.4 with an elastic modulus of about 2-3 GPa.

[0012] It has now been discovered that instead of plasma treating,porous network coatings can be plasma cured, eliminating the need forprior furnace curing.

[0013] However, there remains a need for a method of making a porousnetwork coating having an improved elastic modulus.

SUMMARY OF THE INVENTION

[0014] The present invention produces a coating with a low dielectricconstant and an improved elastic modulus. The method of making thecoating involves providing a porous network coating produced from aresin containing at least 2 Si—H groups. The coating is plasma cured toreduce the amount of Si—H bonds remaining in the coating. Plasma curingof the porous network coating yields a high elastic modulus of greaterthan or about 4 GPa.

[0015] The plasma cured coating can optionally be annealed. Thermalannealing of the plasma cured coating reduces the dielectric constant ofthe coating while maintaining the increase in the elastic modulus ascompared to the elastic modulus before the anneal. The annealingtemperature is typically less than or about 475° C., and the annealingtime is typically no more than or about 180 seconds.

[0016] The annealed, plasma cured coating has a dielectric constant inthe range of from about 1.1 to about 3.5 and an elastic modulus that isgenerally greater than or about 4 GPa, and typically in the range offrom about 4 GPa to about 10 GPa.

[0017] Accordingly, it is an object of the present invention to producecoatings having improved elastic modulus and low dielectric constant.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The manufacture of ultra low dielectric constant coatings havinga dielectric constant of about 1.5 to about 2.4 is described in U.S.Pat. No. 6,231,989, which is incorporated herein by reference for itsteaching on how to produce coatings having ultra low dielectricconstants. This patent describes a process in which pores are introducedinto hydrogen silsesquioxane (HSQ) based films. HSQ based films producedaccording to the method taught in U.S. Pat. No. 6,231,989, which havebeen cured under thermal conditions, contain about 20 to about 60% Si—Hbonds density. When the dielectric constant of the coating is about 2.0,the coating has an elastic modulus of between about 2 and about 3 GPa.The present invention is based on the discovery that plasma curingporous HSQ based films increases the elastic modulus of the film withoutthe necessity of thermally curing the film. Plasma curing reduces theamount of Si—H bonds remaining without losing the low density structureof the film.

[0019] Plasma curing can generate a notable amount of polar species inthe film, which can be undesirable in some applications. The presentinvention is also based on the discovery that applying thermal annealingto plasma cured coatings produces a low dielectric constant, improvedmodulus material.

[0020] The methods of the present invention are particularly applicableto the deposition of coatings on electronic devices or electroniccircuits where they can serve as interlevel dielectric layers, dopeddielectric layers to produce transistor like devices, pigment loadedbinder systems containing silicon to produce capacitor and capacitorlike devices, multilayer devices, 3-D devices, silicon on insulatordevices, super lattice devices, and the like. However, the choice ofsubstrates and devices to be coated by the instant invention is limitedonly by the need for thermal and chemical stability of the substrate atthe temperature and pressure used in the present invention. As such, thecoatings of the present invention can be used on substrates such asplastics including, for example, polyimides, epoxies,polytetrafluoroethylene and copolymers thereof, polycarbonates, acrylicsand polyesters, ceramics, leather, textiles, metals, and the like.

[0021] As used in the present invention, the expression “ceramic”includes ceramics such as amorphous silica and ceramic-like materialssuch as amorphous silica-like materials that are not fully free ofcarbon and/or hydrogen but are otherwise ceramic in character. Theexpressions “electronic device” or “electronic circuit” include, but arenot limited to, silica-based devices, gallium arsenide based devices,silicon carbide based devices, focal plane arrays, opto-electronicdevices, photovoltaic cells and optical devices.

[0022] A porous network coating is needed as a starting material for thepresent invention. One method of making such a porous network coating isdisclosed in U.S. Pat. No. 6,231,989, which is described below.

[0023] The method of producing the porous network coating starts withdepositing a coating on a substrate with a solution comprising a resinmolecule containing at least 2 Si—H groups and a solvent. Those skilledin the art will understand that the resin molecules containing at least2 Si—H groups are repeating units, which form the silicate backbone ofthe resin. The resins containing at least 2 Si—H groups are notparticularly limited as long as the Si—H bonds can be hydrolyzed and atleast partially condensed by the basic catalyst and water to form acrosslinked network that serves as the structure for the porous network.Generally, such materials have the formula:

{R₃SiO_(1/2)}_(a){R₂SiO_(2/2)}_(b){RSiO_(3/2)}_(c){SiO_(4/2)}_(d)

[0024] wherein each R is independently selected from the groupconsisting of hydrogen, alkyl, alkenyl, or aryl groups, or alkyl,alkenyl, or aryl groups substituted with a hetero atom such as ahalogen, nitrogen, sulfur, oxygen, or silicon, and a, b, c, and d aremole fractions of the particular unit and their total is 1, with theproviso that at least 2 R groups per molecule are hydrogen and thematerial is sufficiently resinous in structure to form the desirednetwork. Examples of alkyl groups are methyl, ethyl, propyl, butyl, andthe like, with alkyls of 1-6 carbons being typical. Examples of alkenylgroups include vinyl, allyl, and hexenyl. Examples of aryls includephenyl. Examples of substituted groups include CF₃(CF₂)_(n)CH₂CH₂, wheren=0-6.

[0025] Useful in the present invention are various hydridosiloxaneresins, known as hydrogen silsesquioxane resins, comprising units of theformula HSi(OH)_(x)(OR′)_(y)O_(z/2). In this formula, each R′ isindependently selected from the group consisting of alkyl, alkenyl, oraryl groups, or alkyl, alkenyl, or aryl groups substituted with a heteroatom such as a halogen, nitrogen, sulfur, oxygen, or silicon. Examplesof alkyl groups are methyl, ethyl, propyl, butyl, and the like, withalkyls of 1-6 carbons being typical. Examples of alkenyl groups includevinyl, allyl, and hexenyl. Examples of aryls include phenyl. Examples ofsubstituted groups include CF₃(CF₂)_(n)CH₂CH₂, where n=0-6. When theseR′ groups are bonded to silicon through the oxygen atom, they form ahydrolyzable substituent. In the above formula, x=0 to 2, y=0 to 2, z=1to 3, an x+y+z=3. These resins may be essentially fully condensed(HSiO_(3/2))_(n) where n is 8 or greater, or they may be only partiallyhydrolyzed (i.e., containing some Si—OR′), and/or partially condensed(i.e., containing some Si—OH).

[0026] The structure of the resin containing at least 2 Si—H groups isnot limited. The structure may be what is generally known asladder-type, cage-type, or mixtures thereof. The HSQ resins may containendgroups such as hydroxyl groups, triorganosiloxy groups,diorganohydrogensiloxy groups, trialkoxy groups, dialkoxy groups andothers. The HSQ resin may also contain a small number (e.g., less than10%) of the silicon atoms which have either 0 or 2 hydrogen atomsattached thereto and/or a small number of Si-C groups, such asCH₃SiO_(3/2) or HCH₃SiO_(2/2) groups.

[0027] The resins containing at least 2 Si—H groups and methods fortheir production are known in the art. For example, U.S. Pat. No.3,615,272, to Collins, teaches the production of an essentially fullycondensed hydrogen silsesquioxane resin (which may contain up to 100-300ppm silanol) by a process comprising hydrolyzing trichlorosilane in abenzenesulfonic acid hydrate hydrolysis medium, and then washing theresulting resin with water or aqueous sulfuric acid. Similarly, U.S.Pat. No. 5,010,159 to Bank, teaches a method comprising hydrolyzinghydridosilanes in an arylsulfonic acid hydrate hydrolysis medium to forma resin which is then contacted with a neutralizing agent.

[0028] Other hydridosiloxane resins, such as those described in U.S.Pat. No. 4,999,397, to Frye, and U.S. Pat. No. 5,210,160, to Bergstrom,those produced by hydrolyzing an alkoxy or acyloxy silane in an acidic,alcoholic hydrolysis medium, those described in Japanese Kokai PatentNos. 59-178749, 60-086017, and 63-107122, or any other equivalenthydridosiloxanes, will also function herein.

[0029] Specific molecular weight fractions of the Si—H containing resinsmay also be used. Such fractions and methods for their preparation aretaught in U.S. Pat. No. 5,063,267, to Hanneman, and U.S. Pat. No.5,416,190, to Mine. A typical fraction comprises material wherein atleast 75% of the polymeric species have a number average molecularweight above about 1200, and a more typical fraction comprises materialwherein at least 75% of the polymeric species have a number averagemolecular weight between about 1200 and about 100,000.

[0030] The Si—H containing resins may contain other components as longas these components do not interfere with the integrity of the coating.It should be noted, however, that certain materials may increase thedielectric constant of the coating.

[0031] Ceramic oxide precursors may also be used in combination with theSi—H containing resins. The ceramic oxide precursors useful hereininclude compounds of various metals such as aluminum, titanium,zirconium, tantalum, niobium and/or vanadium, as well as variousnon-metallic compounds, such as those of boron or phosphorus, which maybe dissolved in solution, hydrolyzed and subsequently pyrolyzed atrelatively low temperature to form ceramic oxides. Ceramic oxideprecursors useful herein are described in U.S. Pat. Nos. 4,808,653,5,008,320, and 5,290,394.

[0032] The Si—H containing resins are applied to the substrates assolvent dispersions to form a coating on the substrate (“SiH resincoating”). Solvents that may be used include any agent or mixture ofagents that will dissolve or disperse the resin to form a homogeneousliquid mixture without affecting the resulting coating or the substrate.These solvents can include alcohols, such as ethyl alcohol or isopropylalcohol; aromatic hydrocarbons, such as benzene or toluene; branched orlinear alkanes, such as n-heptane, dodecane, or nonane; branched orlinear alkenes, such as n-heptene, dodecene or tetradecene; ketones,such as methyl isobutyl ketone; esters; ethers, such as glycol ethers;or linear or cyclic siloxanes, such as hexamethyldisiloxane,octamethyldisiloxane, and mixtures thereof, or cyclicdimethylpolysiloxanes; or mixtures of any of the above solvents. Thesolvent is generally present in an amount sufficient todissolve/disperse the resin to the concentration desired forapplication. Typically, the solvent is present in an amount of about 20to about 99.9 wt %, and more typically from about 70 to about 95 wt %,based on the weight of the resin and solvent.

[0033] If desired, other materials can be included in the resindispersion. For instance, the dispersion can include fillers, colorants,adhesion promoters, and the like.

[0034] Specific methods for application of the resin dispersion to thesubstrate include, but are not limited to, spin coating, dip coating,spray coating, flow coating, screen printing, or others. A typicalmethod is spin coating.

[0035] At least about 5 volume % of the solvent should remain in the SiHresin coating until the resin is contacted with the basic catalyst andwater. This solvent forms the pores of the porous network coating as theSi—H bonds are hydrolyzed and condensed. In some embodiments, it may betypical that at least about 10 volume % solvent remains, while inothers, it may be typical that at least about 15 volume % solventremains, and in still others, it may be typical that at least about 25volume % solvent remains.

[0036] The method of retaining the solvent is not particularlyrestricted. In a typical embodiment, a high boiling point solvent can beused alone or as a co-solvent with one of the solvents described above.In this manner, processing the resin dispersion as described above undernormal conditions allows for at least about 5% residual solventremaining. Typical high boiling solvents in this embodiment are thosewith boiling points above about 175° C. including hydrocarbons, aromatichydrocarbons, esters, ethers, and the like. Examples of specificsolvents which can be used in this embodiment include saturatedhydrocarbons, such as dodecane, tetradecane, hexadecane, etc.,unsaturated hydrocarbons such as dodecene, tetradecene, etc., xylenes,mesitylene, 1-heptanol, dipentene, d-limonene, tetrahydrofurfurylalcohol, mineral spirits, 2-octanol, stoddard solvent, Isopar H™,diethyl oxalate, diamyl ether, tetrahydropyran-2-methanol, lactic acidbutyl ester, isooctyl alcohol, propylene glycol, dipropylene glycolmonomethyl ether, diethylene glycol diethyl ether, dimethyl sulfoxide,2,5-hexanedione, 2-butoxyethanol acetate, diethylene glycol monomethylether, 1-octanol, ethylene glycol, Isopar L™, dipropylene glycolmonomethyl ether acetate, diethylene glycol monoethyl ether,N-methylpyrrolidone, ethylene glycol dibutyl ether, gamma-butyrolactone,1,3-butanediol, diethylene glycol monomethyl ether acetate, trimethyleneglycol, triethylene glycol dimethyl ether, diethylene glycol monoethylether acetate, alpha-terpineol, n-hexyl ether, kerosene,2-(2-n-butoxyethoxy)ethanol, dibutyl oxalate, propylene carbonate,propylene glycol monophenyl ether, diethylene glycol, catechol,diethylene glycol monobutyl ether acetate, ethylene glycol monophenylether, diethylene glycol dibutyl ether, diphenyl ether, ethylene glycolmonobenzyl ether, hydroquinone, sulfolane, and triethylene glycol.Hydrocarbon solvents are particularly preferred.

[0037] The above processing (i.e., primarily deposition of the SiH resincoating solution) can be done in an environment that inhibits solventevaporation prior to contact with the basic catalyst and water. Forexample, the spin coating can be performed in a closed environment suchthat the subsequent steps (i.e., contact with the basic catalyst andwater) can occur before the solvent is completely evaporated.

[0038] The SiH resin coating containing at least about 5 volume %solvent is then contacted with a basic catalyst and water. Examples ofbasic catalysts include ammonia, ammonium hydroxide, as well as amines.The amines useful herein may include primary amines (RNH₂), secondaryamines (R₂NH), and/or tertiary amines (R₃N) in which R is independentlya saturated or unsaturated aliphatic, such as methyl, ethyl, propyl,vinyl, allyl, ethynyl, etc.; an alicyclic, such as cyclohexylmethyl; anaromatic, such as phenyl; a substituted hetero atom, such as oxygen,nitrogen, sulfur, etc.; or compounds in which the nitrogen atom is amember of a heterocyclic ring such as quinoline, pyrrolidine, orpyridine. In addition, any of the above amine compounds may besubstituted with other hydrocarbon and/or hetero containing groups toform compounds such as diamines, amides, etc. Finally, it is alsocontemplated that compounds, which are converted to amines under thereactions conditions used, would function in an equivalent manner. Forexample, a compound such as an ammonium salt that yields an amine upondissolution would provide the desired catalytic effect.

[0039] Examples of the amines that may used herein include methylamine,ethylamine, butylamine, allylamine, cyclohexylamine, aniline,dimethylamine, diethylamide, dioctylamine, dibutylamine,methylethylamine, saccharin, piperidine, trimethylamine, triethylamine,pyridine, diethyl toluidene ethylmethylpropylamine, imidazole, cholineacetate, triphenyl phosphene analine, trimethylsilylimidazole,ethylenediamine, diethylhydroxylamine, triethylenediamine,n-methylpyrolidone, etc.

[0040] The basic catalyst can generally be used at any concentrationsufficient to catalyze hydrolysis of the Si—H bonds. Generally,concentrations of the basic catalyst can be from about 1 ppm to about100 wt % based on the weight of the resin, depending on the basiccatalyst.

[0041] The water used can be that present in the ambient environment(e.g., > about 25% relative humidity), the ambient environment can besupplemented with additional water vapor (e.g., relative humidity up toabout 100%), water can be used as a liquid, or a compound whichgenerates water under the reaction conditions can be used.

[0042] Contact of the SiH resin coating with the basic catalyst andwater can be accomplished by any means practical or desirable. Forinstance, the SiH resin coating can be contacted with vapors of thebasic catalyst and water vapor. Alternatively, the SiH resin coating canbe contacted with the basic catalyst and water in the liquid state, suchas by immersing the coating in an ammonium hydroxide solution.

[0043] The SiH resin coating is typically exposed to an environmentcomprising the basic catalyst and water in the vapor state, moretypically ammonia and water vapor. For instance, the SiH resin coatedsubstrate may be placed in a container and the appropriate environmentintroduced therein, or a stream of the basic catalyst and water may bedirected at the SiH resin coating.

[0044] The method used to generate the basic catalyst and waterenvironment is generally not significant in the present embodiment.Methods such as bubbling the basic catalyst (e.g., ammonia gas) throughwater or ammonium hydroxide solutions (to control the amount of watervapor present), heating a basic catalyst and water, or heating water andintroducing the basic catalyst gas (e.g., ammonia gas) are allfunctional herein. It is also contemplated that methods, which generatebasic catalyst vapors in situ, such as the addition of water to aminesalts, or the addition of water to a silazane such ashexamethyldisilazane, will also be effective.

[0045] The basic catalyst used may be at any concentration desired. Forexample, the concentration may be from about 1 ppm up to a saturatedatmosphere.

[0046] The exposure can be at any temperature desired from roomtemperature up to about 300° C. A temperature in the range of from about20° C. to about 200° C. is typical, with a range of from about 20° C. toabout 100° C. being more typical.

[0047] The SiH resin coating should be exposed to the basic catalyst andwater environment for the time necessary to hydrolyze the Si—H groups toform silanols (Si—OH) and for the silanols to at least partiallycondense to form Si—O—Si bonds. Generally, exposures of up to about 20minutes are typical, with exposures of at least about 1 second up toabout 5 minutes being more typical. If the coatings are to be used as adielectric layer, it is generally typical to have a shorter exposure, aslonger exposures tend to increase the dielectric constant of thecoating.

[0048] When the coating is exposed to the basic catalyst and water inthe liquid state, the exposure is usually conducted by immersing thecoated substrate in a solution. Other equivalent methods can be used,such as flushing the coating with a basic catalyst and water solution.In addition, vacuum infiltration may also be used to increasepenetration of the basic catalyst and water into the coating.

[0049] The basic catalyst solution used in this embodiment may be at anyconcentration desired. Generally when ammonium hydroxide is used, aconcentrated aqueous solution of between about 28 and about 30% istypical since the duration of exposure is thereby shortened. When dilutesolutions are used, the diluent is generally water.

[0050] Exposure to the basic catalyst and water solution in thisembodiment may be conducted at any temperature and pressure desired.Temperatures from about room temperature (20-30° C.) up to about theboiling point of the basic catalyst solution, and pressures from belowto above atmospheric are all contemplated herein. From a practicalstandpoint, it is typical that the exposure occur at about roomtemperature and at about atmospheric pressure.

[0051] The resin coating is exposed to the basic catalyst solution inthis embodiment for the time necessary to hydrolyze the Si—H groups toform silanols (Si—OH) and for the silanols to at least partiallycondense to form Si—O—Si bonds. Generally, exposures of up to about 2hours are typical, with exposures of at least about 1 second up to about15 minutes being more typical.

[0052] Alternatively, the coating may be exposed to both a liquid basiccatalyst and water environment (e.g., ammonium hydroxide) and a gaseousbasic catalyst and water vapor environment (ammonia gas and watervapor). The exposures may be either sequential or simultaneous, and aregenerally under the same conditions as those described above.

[0053] After the resin is exposed to one of the above environments, thesolvent is then removed from the coating. This can be accomplished byany desired means, including but not limited to, heating the coating,and by vacuum. When the solvent is removed by heating the coating,condensation of the remaining silanols may be facilitated.

[0054] The coating produced by this process can be used as the startingmaterial (“porous network coating”) in the present invention. In atypical procedure to produce a porous network coating, a substrate iscoated with the Si—H containing resin and solvent in a manner whichensures that at least about 5 volume % of the solvent remains in thecoating. The coating is then exposed to the basic catalyst and water,and the solvent is evaporated.

[0055] Another method of making such a porous network coating isdisclosed in U.S. Pat. No. 6,143,360 to Zhong, entitled METHOD FORMAKING NANOPOROUS SILICONE RESINS FROM ALKYLHYDRIDOSILOXANE RESINS. Themethod comprises contacting a hydridosilicon containing resin with a1-alkene comprising about 8 to about 28 carbon atoms in the presence ofa platinum group metal-containing hydrosilation catalyst, effectingformation of an alkylhydridosiloxane resin where at least about 5percent of the silicon atoms are substituted with at least one hydrogenatom and heating the alkylhydridosiloxane prepared at a temperaturesufficient to effect curing and thermolysis of alkyl groups from thesilicon atoms, thereby forming a nanoporous silicone resin.

[0056] Although porous network coatings having low dielectric constantsare desirable, it would be advantageous to have a coating with a higherelastic modulus.

[0057] In order to raise the elastic modulus of the porous networkcoating, it is exposed to a plasma cure. The plasma cure can be done byradio frequency (RF), inductive coupled, RF capacitive coupled, helicalresinator, microwave downstream, and microwave electron cyclotronresonance (ECR) plasma.

[0058] In a typical plasma curing process, the wafer is quickly heatedin a rapid temperature ramp-up step to the desired temperature, and thewafer is plasma cured.

[0059] The exact conditions for the plasma cure depend upon what type ofplasma cure is being used. Examples of typical microwave plasma cureconditions for a 200 mm wafer are shown below. Microwave Plasma Power:1000 W-2000 W Wafer Temperature: 80° C.-350° C. Process Pressure: 1.0torr-6.0 torr Plasma Cure Time: >15 seconds Plasma Gases: H₂/N₂/CF₄/O₂O₂ flow rate: 0-4000 sccm CF₄ flow rate: 0-400 sccm H₂/N₂ Gas Mixtureflow rate: >0-4000 sccm

[0060] The plasma cured porous network coatings of the present inventionhave improved chemical stability and improved dimensional stability. Byimproved chemical stability, we mean that the coatings are moreresistant to chemicals, such as cleaning solutions and chemicalpolishing solutions, and plasma damaging during photoresist ashing anddry etching processes.

[0061] However, plasma cure can generate a notable amount of polarspecies in the film.

[0062] The plasma cured coatings can be annealed using any type ofthermal exposure to reduce the dielectric constant, if desired. Forexample, the plasma cured coatings can be placed in a conventional ovenuntil the polar species are removed, such as at 450° C. for 30 minutes.Another process which can be used involves annealing the plasma curedcoatings in a Rapid Thermal Processing (RTP) chamber in order to reducethe dielectric constant. The plasma cured coating is annealed at atypical temperature for a sufficient time, and cooled to about 100° C.

[0063] Typical operating conditions for the RTP process are shown below.Ramp rate: 150° C./sec Wafer Temperature: 350-450° C. Annealing Time:<180 seconds

[0064] The dielectric constant of the annealed, plasma cured coatings isreduced as compared to the plasma cured porous network coatings. Thedielectric constant of the annealed, plasma cured coatings is typicallyin the range of from about 1.1 to about 3.5 and more typically in therange of from about 2 to about 2.5.

[0065] The elastic modulus of the annealed, plasma cured coatings isincreased as compared to a furnace (thermally) cured coating which wouldhave an elastic modulus of between about 2.0 and about 3.0 when thedielectric constant is about 2.0. This increase in the elastic modulusis typically greater than or about 50%, and more typically greater thanor about 100%. Typically, the elastic modulus of the annealed, plasmacured coating is greater than or about 4 GPa, and more typically betweenabout 4 GPa and about 10 GPa.

[0066] In order that the invention may be more readily understood,reference is made to the following examples, which are intended toillustrate the invention, but not limit the scope thereof.

EXAMPLE 1

[0067] Porous network coatings were produced from hydrogensilsesquioxane resin by spinning onto silicon wafers and treating withNH₃ followed by 1 minute 150° C. hotplate thermal treatments. The plasmaconversion was done in an Axcelis Fusion Gemini® ES plasma asher. Afterthe plasma conversion, porous silica films with low dielectric constantand high modulus have been obtained. The results are shown in Table 1.

[0068] The plasma conditions were 2-4 torr in pressure. The temperatureswere controlled between 195-230° C. The forming gas was N₂/H₂/CF₄. Theplasma power and gas flow data are listed in Table 1.

[0069] The results indicate that, after plasma curing, the dielectricconstants are in a range of 2.0 to 2.8. The plasma conditions at 210° C.yielded films of lower dielectric constants, lower than 2.4. The filmsprocessed at 195, 225, and 230° C. showed dielectric constants higherthan 2.4. The modulus of the plasma cured films are from 6 to 9 GPa. Theplasma curing process took off approximately 10% of the film thickness.However, the uniformity of the plasma cured film is typically within 2%.The FTIR spectra suggest that Si—H bonds were completely removed fromthe films during the plasma curing at pressures of 2-3 torr, implyingthat porous silica films were made from the plasma curing process.Typically, the films with the dielectric constants of 2.0-2.3 includeless than 1% Si—OH. TABLE 1 Plasma Cure of Films (Example 1) Pre-PlasmaHeating Plasma Cure Conditions Time Pressure Temperature Time PressureTemperature Power H₂N₂ CF₄ Modulus Refractive Thickness Wafer (sec)(torr) (° C.) (sec) (torr) (° C.) (W) (sccm) (sccm) Dk (GPa) Index (Å) 1120 2.0 210 90 2.0 210 1800 2000 100 2.30 7.3 1.202 4302 2 120 3.0 21090 3.0 210 1800 2000 100 2.13 7.0 1.196 4265 3 120 3.0 210 90 3.0 2101800 2000 100 2.27 8.2 1.258 3628 4 120 2.5 210 90 2.5 210 1800 2000 1002.29 7.9 1.247 3671 5 120 4.0 210 90 4.0 210 1800 2000 100 2.16 6.71.205 3676 6 120 4.0 210 90 4.0 210 1800 2000 100 2.24 6.5 1.182 4403 7120 2.5 230 90 2.5 230 1800 2000 100 2.80 8.8 1.244 3652 8 120 2.0 22590 2.0 225 1800 2000 100 2.88 7.6 1.203 4442 9 120 2.5 225 90 2.5 2251800 2000 100 2.57 7.2 1.212 4315 10 120 3.0 225 90 3.0 225 1800 2000100 2.43 7.2 1.197 4400 11 120 2.0 195 90 2.0 195 1800 2000 100 2.59 6.81.215 4351 12 120 2.5 195 90 2.5 195 1800 2000 100 2.74 7.3 1.216 431513 120 3.0 195 90 3.0 195 1800 2000 100 2.73 7.0 1.203 4296 14 0 2.5 21090 2.5 210 1800 2000 100 2.10 6.9 1.216 3733 15 0 3.0 210 90 3.0 2101800 2000 100 2.02 6.6 1.212 3766

EXAMPLE 2

[0070] Porous network coatings were produced from hydrogensilsesquioxane by spinning onto silicon wafers and treating with NH₃followed by 1 minute 150° C. hotplate thermal treatments. The NH₃ agingtime was ½ to ⅔ of standard recipes specified in both the TEL spin tooland the DNS spin tool. The plasma conversion was done in an AxcelisFusion Gemini® ES plasma asher. After the plasma conversion, poroussilica films with low dielectric constant and high modulus have beenobtained. The results are shown in Table 2.

[0071] The plasma conditions were 2-4 torr in pressure. The temperatureswere controlled at 210° C. The forming gas was N₂/H₂/CF₄. The plasmapower and gas flow data are listed in Table 2.

[0072] The plasma curing can also convert the initial films into poroussilica films even if the initial films were aged for a short time undermoist NH₃. The plasma cured films with less than standard aging timeshow dielectric constants under 2.3. The modulus values are from 5.7 to9 GPa. Again, from FTIR spectra, Si—H bonds were removed during theplasma curing so that porous silica films were obtained. The Si—OH levelin these films is typically less than 1%. TABLE 2 Plasma Cure of Films(Example 2) Pre-Plasma Heating Plasma Cure Conditions Time PressureTemperature Time Pressure Temperature Power H₂N₂ CF₄ Modulus RefractiveThickness Wafer (sec) (torr) (° C.) (sec) (torr) (° C.) (W) (sccm)(sccm) Dk (GPa) Index (Å) 2/3 NH₃ Treatment in TEL 1 120 3.0 210 90 3.0210 1800 2000 100 2.60 8.8 1.258 3521 2 120 2.5 210 90 2.5 210 1800 2000100 2.32 9.0 1.261 3577 3 120 2.5 210 90 2.5 210 1800 2000 100 2.27 8.21.258 3628 4 120 4.0 210 90 4.0 210 1800 2000 100 2.23 5.7 1.214 3570 5120 2.5 230 90 2.5 230 1800 2000 100 2.24 8.5 1.257 3654 6 60 2.5 210 902.5 210 1800 2000 100 2.21 9.1 1.254 4599 7 0 2.5 210 90 2.5 210 18002000 100 2.24 9.0 1.270 3550 1/2 NH₃ Treatment in DNS 8 120 2.5 210 902.5 210 1800 2000 100 2.27 8.4 1.219 4269 9 120 3.0 210 90 3.0 210 18002000 100 2.39 8.0 1.218 4186

EXAMPLE 3

[0073] Porous network coatings were produced from hydrogensilsesquioxane by spinning onto silicon wafers and treating withexcessive NH₃ followed by 1 minute 150° C. hotplate thermal treatments.The NH₃ aging time was twice as long as that specified in the standardrecipes for both the TEL spin tool and the DNS spin tool. The plasmaconversion was done in an Axcelis Fusion Gemini® ES plasma asher. Theresults are shown in Tables 3A and 3B.

[0074] The plasma conditions were 2.5-3 torr in pressure. Thetemperatures were controlled at 210° C. The forming gas was N₂/H₂/CF₄.The plasma power and gas flow data are listed in Tables 3A and 3B.

[0075] After longer NH₃ aging, the dielectric constants of the plasmacured porous films are 2.5 or higher, and the moduli are approximately7-8 GPa. The Si—OH content is typically around 1.5-2.5%, as calculatedfrom FTIR spectra. The Si—H bonds were completely removed.

[0076] In Examples 1-3, the infrared spectra of the annealed, plasmacured coatings that were thermally annealed by heating using RTP arevirtually identical to those coatings that were thermally annealed byother heating methods. The features in the spectra indicate that thisplasma cured film is silica in nature. The SiOH content is less than 1weight percent as calculated from the infrared spectra. The refractiveindex (RI) of the RTP annealed coatings (1.20 to 1.22) is consistentwith the RI value of coatings that were thermally annealed by otherheating methods. The elastic modulus of the plasma cured coatings thatwere thermally annealed by RTP can be two or three times higher (as highas 7-8 GPa) than the initial elastic modulus. The dielectric constantsof these coatings range from 2.1 to 2.3. TABLE 3A Long Aging Time 2 ×Standard Time on the DNS Tool (Example 3) Pre-Plasma Heating Plasma CureConditions Time Pressure Temperature Time Pressure Temperature PowerH₂N₂ CF₄ Modulus Refractive Thickness Wafer (sec) (torr) (° C.) (sec)(torr) (° C.) (W) (sccm) (sccm) Dk (GPa) Index (Å) 1 120 3.0 210 90 3.0210 1800 2000 100 2.63 8.0 1.197 4369 2 120 2.5 210 90 2.5 210 1800 2000100 2.53 8.2 1.197 4685

[0077] TABLE 3B Long Aging Time 1.5 × Standard Time on the DNS Tool(Example 3) Pre-Plasma Heating Plasma Cure Conditions Time PressureTemperature Time Pressure Temperature Power H₂N₂ CF₄ Modulus RefractiveThickness Wafer (sec) (torr) (° C.) (sec) (torr) (° C.) (W) (sccm)(sccm) Dk (GPa) Index (Å) 3 120 3.0 210 90 3.0 210 1800 2000 100 2.548.4 1.200 4429 4 120 2.5 210 90 2.5 210 1800 2000 100 2.53 8.7 1.1994454

[0078] By the above methods, a thin (less than 5 microns) SiO₂containing coating is produced on the substrate. The coating has animproved elastic modulus. Furthermore, with the annealing step, thecoating can have an improved elastic modulus and a low dielectricconstant.

[0079] The coating smooths the irregular surfaces of various substratesand has excellent adhesion. In addition, the coating may be covered byother coatings, such as further SiO₂ coatings, SiO₂/modifying ceramicoxide layers, silicon containing coatings, carbon containing coatings,and/or diamond like coatings.

[0080] These coatings posses low defect density and are useful onelectronic devices as dielectric layers in, for example, multilayerdevices.

[0081] While certain representative embodiments and details have beenshown for purposes of illustrating the invention, it will be apparent tothose skilled in the art that various changes in the compositions andmethods disclosed herein may be made without departing from the scope ofthe invention, which is defined in the appended claims.

What is claimed is:
 1. An SiO₂-containing plasma cured coating having afirst dielectric constant and having a first elastic modulus, thecoating being formed by providing a porous network coating produced froma resin molecule containing at least 2 Si—H groups; and plasma curingthe porous network coating to reduce an amount of Si—H bonds.
 2. TheSiO₂-containing plasma cured coating of claim 1 being formed by plasmacuring the porous network coating for between about 15 and about 120seconds.
 3. The SiO₂-containing plasma cured coating of claim 1 beingformed by plasma curing the porous network coating at a temperature lessthan or about 350° C.
 4. The SiO₂-containing plasma cured coating ofclaim 1 being formed by plasma curing the porous network coating at atemperature between about 80 and about 280° C.
 5. The SiO₂-containingplasma cured coating of claim 1 being formed by plasma curing the porousnetwork coating at a temperature between about 195 and about 230° C. 6.The SiO₂-containing plasma cured coating of claim 1 being formed byannealing the plasma cured coating to produce an annealed, plasma curedcoating having a second dielectric constant which is less than the firstdielectric constant and having a second elastic modulus which iscomparable to the first elastic modulus.
 7. The SiO₂-containing plasmacured coating of claim 6 being formed by annealing the plasma curedcoating at a temperature less than or about 475° C.
 8. TheSiO₂-containing plasma cured coating of claim 6 being formed byannealing the plasma cured coating at a temperature between about 350and about 450° C.
 9. The SiO₂-containing plasma cured coating of claim 6being formed by annealing the plasma cured coating for no more than orabout 180 seconds.
 10. The SiO₂-containing plasma cured coating of claim6 wherein the second elastic modulus of the annealed, plasma curedcoating is greater than or about 4 GPa.
 11. The SiO₂-containing plasmacured coating of claim 6 wherein the second elastic modulus of theannealed, plasma cured coating is between about 4 and about 10 GPa. 12.The SiO₂-containing plasma cured coating of claim 6 wherein the seconddielectric constant of the annealed, plasma cured coating is betweenabout 1.1 and about 3.5.
 13. The SiO₂-containing plasma cured coating ofclaim 6 wherein the second dielectric constant of the annealed, plasmacured coating is between about 2 and about 2.5.
 14. An annealed,SiO₂-containing plasma cured coating having a dielectric constantbetween about 1.1 and about 3.5 and an elastic modulus greater than orabout 4 GPa, the coating being formed by providing a porous networkcoating produced from a resin molecule containing at least 2 Si—Hgroups; plasma curing the porous network coating to reduce an amount ofSi—H bonds and to produce a plasma cured coating; and annealing theplasma cured coating.
 15. The annealed, SiO₂-containing plasma curedcoating of claim 14 having an elastic modulus between about 4 and about10 GPa.
 16. The annealed, SiO₂-containing plasma cured coating of claim14 having a dielectric constant between about 2 and about 2.5.
 17. Anelectronic device containing a plasma cured coating, the coating beingformed by providing a porous network coating produced from a resinmolecule containing at least 2 Si—H groups; and plasma curing the porousnetwork coating to reduce an amount of Si—H bonds.
 18. An electronicdevice containing an annealed, plasma cured coating, the coating beingformed by providing a porous network coating produced from a resinmolecule containing at least 2 Si—H groups; plasma curing the porousnetwork coating to reduce an amount of Si—H bonds and to produce aplasma cured coating; and annealing the plasma cured coating.
 19. Anelectronic circuit containing a plasma cured coating, the coating beingformed by providing a porous network coating produced from a resinmolecule containing at least 2 Si—H groups; and plasma curing the porousnetwork coating to reduce an amount of Si—H bonds.
 20. An electroniccircuit containing an annealed, plasma cured coating, the coating beingformed by providing a porous network coating produced from a resinmolecule containing at least 2 Si—H groups; plasma curing the porousnetwork coating to reduce an amount of Si—H bonds and to produce aplasma cured coating; and annealing the plasma cured coating.
 21. Asubstrate having a plasma cured coating, the coating being formed byproviding a porous network coating produced from a resin moleculecontaining at least 2 Si—H groups; and plasma curing the porous networkcoating to reduce an amount of Si—H bonds.
 22. A substrate having anannealed, plasma cured coating, the coating being formed by providing aporous network coating produced from a resin molecule containing atleast 2 Si—H groups; plasma curing the porous network coating to reducean amount of Si—H bonds and to produce a plasma cured coating; andannealing the plasma cured coating.
 23. A porous SiO₂-containing plasmacured coating having a dielectric constant between about 1.1 and about3.5 and an elastic modulus between about 4 and about 10 GPa.
 24. Aporous SiO₂-containing plasma cured coating having a dielectric constantbetween about 2 and about 2.9 and an elastic modulus between about 5.7and about 9.1 GPa.
 25. A porous SiO₂-containing plasma cured coatingproduced from a resin molecule containing at least 2 Si—H groups, thecoating having a dielectric constant between about 1.1 and about 3.5 andan elastic modulus between about 4 and about 10 GPa.
 26. A porousSiO₂-containing plasma cured coating produced from a resin moleculecontaining at least 2 Si—H groups, the coating having a dielectricconstant between about 2 and about 2.9 and an elastic modulus betweenabout 5.7 and about 9.1 GPa.
 27. The porous SiO₂-containing plasma curedcoating of claim 25 wherein the resin molecule has the formula:{R₃SiO_(1/2)}_(a){R₂SiO_(2/2)}_(b){RSiO_(3/2)}_(c){SiO_(4/2)}_(d)wherein each R is independently selected from the group consisting ofhydrogen, alkyl, alkenyl, and aryl groups or alkyl, alkenyl, and arylgroups substituted with halogen, nitrogen, oxygen sulfur or siliconatoms, with the proviso that at least 2 R groups are hydrogen.
 28. Theporous SiO₂-containing plasma cured coating of claim 25 wherein theresin molecule comprises a hydrogen silsesquioxane resin molecule of thestructure selected from (HSiO_(3/2))_(n), a polymer having units of theformula HSi(OH)_(a)O_(3-x/2) and a polymer having units of the formulaHSi(OH)_(x)(OR)_(y)O_(z/2), wherein each R is independently an organicgroup which, when bonded to silicon through the oxygen atom, forms ahydrolyzable substituent, a=0-2, x=0-2, y=0-2, z=1-3, x+y+z=3, n is aninteger greater than 3 and the average value of y over all of the unitsof the polymer is greater than 0.